1. Field of the Invention
The present invention relates to surfactant-containing seamless capsules and a method for producing them. More specifically, it relates to seamless capsules containing a surfactant component and an oily component, which can be used in the fields of pharmaceuticals, foods, luxury foods, bath additives and detergents, and to a method for producing such surfactant-containing seamless capsules.
2. Description of the Related Art
There have traditionally been produced seamless capsules containing an oily component, such as a vegetable oil, but no surfactants. This type of seamless capsules is prepared by means of interfacial tension, as disclosed in Japanese Patent Examined Publication No. 3700/1961. Therefore, when the liquid content contains a surfactant component having a high HLB value, the encapsulation has been difficult because of considerable reduction in the interfacial tension between the content liquid and the film-forming liquid.
Japanese Patent Laid-Open Nos. 227519/1986 and 238519/1989 disclose capsules containing a nonionic surfactant having a relatively high HLB value. However, because these capsules are produced by encapsulation using a capsule-filling machine, their film has a seam, which results in problems of leakage of the contents, and dissolution speed variation among capsules due to uneven distribution of mean film thickness, as well as undesirable appearance.
On the other hand, Japanese Patent Examined Publication No. 39193/1978 and Japanese Patent Laid-Open No. 99177/1980 disclose seamless capsules having a multiple-layer structure obtained using a multiple-nozzle, but these capsules contain no surface-active component. Also, Japanese Patent Laid-Open No. 52639/1991 discloses seamless capsules wherein surface-active, lower fatty acid esters of sucrose is present between the hydrophilic substance and the film. However, this disclosure does not deal with capsules containing a surfactant component and an oily component as the content.
Furthermore, Japanese Patent Laid-Open No. 13508/1983 discloses seamless capsules of a pharmaceutical composition containing a dispersion of both a practically water-insoluble drug and a polyglycerol fatty acid ester in a liquid oil. Also, Japanese Patent Laid-Open No. 31352/1993 discloses seamless capsules containing a hydrophilic substance and a method for production thereof. However, these proposals pose problems such as functional reduction due to insufficient adsorption of the oily component to the skin because of its separation from water when the capsules are applied to bath additives and other uses in water. In other words, these publications give no disclosure of capsules wherein the content liquid can be substantially emulsified and dispersed in water, or capsules wherein the surfactant component is substantially uniformly dispersed or dissolved in the oily component, and no disclosure of a method for production thereof.
As stated above, there has not been known any seamless capsules containing a surfactant component and an oily component as the contents of the capsules wherein the liquid content is excellently emulsifiable and dispersible in water or the surfactant component is excellently dispersible or soluble in the oily component, or any method for production of such capsules. In particular, in the fields of bath additives and detergents, where high emulsifiability and dispersibility are required for the liquid content, there has been a need for the development of such seamless capsules and a method for production thereof.